1. Field of the Invention
The present invention relates to a lubricating structure for an internal combustion engine, which is suitable for suppressing the machining cost, miniaturizing the engine, and changing the amount of oil to be supplied to portions to be lubricated.
2. Description of Background Art
A relief valve opened when the pressure in an oil passage in an internal combustion engine exceeds a specific value has been known, for example, from Japanese Patent Laid-open No. Hei 9-144517 entitled xe2x80x9cTransmission Lubricating Structure for Four-cycle Enginexe2x80x9d.
The transmission lubricating structure described in the above document is configured, as shown in FIG. 3 of the Japanese Laid-open publication, such that an oil pump 34 is communicated to an oil filter 35 via an oil passage 39, and a relief valve 44 is provided in an oil passage branched from the oil passage 39.
In the above-described technique, since the branched oil passage connected to the relief valve 44 is provided separately from the oil passage 39 for supplying oil to portions to be lubricated of an engine 7 via the oil filter 35, the number of machining steps for forming the branched oil passage and the machining cost required therefor are increased. In addition, since a space is required for providing the branched oil passage and the relief valve 44, the size of the engine 7 is enlarged.
Further, the flow rate of oil supplied from the oil pump 34 to the oil filter 35 side via the oil passage 39 can be changed by the relief valve 44. However, if it is intended to change the amount of oil to be supplied to portions to be lubricated on the downstream side from the relief valve 44, the configuration of the lubricating structure must be changed on a large-scale. For example, the existing oil pump 34 must be replaced with a new oil pump having a different displacement, or the existing oil passage 39 must be replaced with a new oil passage having a different crosssection.
An object of the present invention is to provide a lubricating structure for an internal combustion engine, which is capable of (1) suppressing the machining cost and miniaturizing the engine, and (2) easily changing the amount of oil to be supplied to portions to be lubricated.
To achieve the above object, according to the present invention, there is provided a lubricating structure for an internal combustion engine including an oil supply passage for supplying oil from an oil pump to portions to be lubricated and a relief valve which is opened for relieving part of the oil into a relief passage when the pressure in the oil supply passage exceeds a specific valve, characterized in that the relief valve is interposed in the oil supply passage, and the relief valve internally includes a passage for supplying oil from one oil supply passage to another oil supply passage.
The relief valve, which is interposed in the oil supply passage, allows the supply of oil from one oil supply passage to another oil passage through the passage provided in the relief valve. Such a relief valve is opened for relieving part of the oil in the relief passage when the pressure in the oil supply passage exceeds a specific value.
As a result, it is possible to eliminate the need for providing a branched oil passage for the relief valve and hence to reduce the number of machining steps and lower the machining cost.
Further, since a space for disposing a branched oil passage is not required and since an increase in the space for disposing of the relief valve can be reduced, the engine can be miniaturized.
According to the present invention, a throttle structure for restricting the flow rate of the oil to be supplied to the portions to be lubricated by the relief valve is provided in the oil supply passage.
The relief valve opened when the pressure in the oil supply passage exceeds a specific value is provided in the oil supply passage, and the throttle structure for restricting the flow rate of the oil to be supplied to the portions to be lubricated is provided in the relief valve.
As a result, the amount of oil to be supplied to the portions to be lubricated can be easily changed only by changing the throttle structure.
According to the present invention, the throttle structure is configured as an orifice hole opened in a valve body of the relief valve.
The throttle structure is configured as the orifice hole opened in the relief valve.
As a result, since the valve body of the relief valve serves as the throttle structure, the lubricating structure can be simplified and the number of parts can be reduced, as compared with the case in which the valve body and a member in which the orifice hole is opened are provided separately from each other.
Further, the amount of oil to be supplied to the portions to be lubricated can be easily changed by replacing an existing valve body with a new valve body having an orifice whose cross-section is suitably changed from that of the orifice of the existing valve body.
According to the present invention, the relief valve is provided in an oil supply passage passing through a portion near a power transmission member in the internal combustion engine. As a result, the power transmission member can be lubricated with the oil which has flowed out of the relief passage of the relief valve.
This makes it possible to eliminate the need of providing any special oil passage for supplying oil to the power transmission member.
According to the present invention, the power transmission member is a cam chain hung between a crank shaft and a cam shaft in the internal combustion engine, and the relief valve is provided in such a manner so as to cross a cam chain chamber for containing the cam chain.
The power transmission member is configured as the cam chain hung between the crank shaft and the cam shaft in the internal combustion engine, and the relief valve is provided in such a manner so as to cross a cam chain chamber for containing the cam chain.
As a result, the cam chain can be lubricated with the oil which has flowed out of the relief passage of the relief valve. Further, since the oil adhering on the cam chain can be scattered to a cylinder head, it is possible to lubricate respective portions of the cylinder head with the scattered oil.
Further, since the relief valve serves as a pipe member crossing the cam chain chamber, it is possible to reduce the number of parts as compared with the case in which the relief valve and the pipe member are provided separately from each other, and hence to reduce the manufacturing cost of the engine.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.